Usually, serial numbers can be found engraved on the back of the watch case. The serial numbers identify the age of the watch. Some watches have the serial numbers on the inside movement. If so, the serial number is inside the movement and has a number and symbol.
The serial numbers are used for identification purposes only. The newer Bulova watches use a system in which the manufacturing year is identified at the beginning of the serial number. In 1948, watches started to be labeled A8. Watches before 1948 did not have dating systems on them. Charts with Bulova dating codes can be found online.